CEP-controlled non-adiabatic transitions visualized by photoelectron spectroscopy and attosecond transient absorption spectroscopy in LiH

We steer the LiH molecule towards a target dissociation channel by using few cycle CEP stabilized IR pulses and follow the dynamics using both time-resolved photoelectron spectroscopy and attosecond transient absorption spectroscopy.
Control of the molecular reactivity can be achieved using intense few-cycle pulses [1]. These pulses build coherent superposition of neutral excited electronic states (ES) and can induce photoionization of the molecule. Fully accounting for the effect of the few-cycle pulse and for the interaction with the ionization continuum, we investigate how the CEP can be used
to steer the branching ratio between the different dissociation channels in the LiH molecule. The coherent superpositions of ES built upon excitation are equivalent to a non-stationary electronic and nuclear wave packet [2]. The pulses Carrier-Envelope Phase (CEP) can be imprinted on the phase of the wave packet components [3] and on the phase of the electron density oscillation resulting from the excitation[4], even in the presence of photoionization. The subsequent nuclear dynamics involves non-adiabatic (NA) amplitude transfers between the ES of the superposition. They are governed by the relative phase between the components of the wave packet at the time and location of NA interaction[5,6], affecting the final state of the molecule.
By numerically integrating the time-dependent Schrödinger equation on a grid along the nuclear coordinate for several potential energy curves coupled both by the interaction with the electric field and by NA couplings, and using the partitioning method to account for photoionization, we computed the photoexcitation and photoionization coupled electronic- nuclear quantum dynamics of the oriented LiH molecule excited by a one-cycle CEP stabilized IR pulse polarized along the molecular axis. The pulse builds a coherent superposition of the 10 Σ states below the IP. We show that the branching ratio 2Σ / 3Σ can be driven from 0.6 to 6 depending on the value of the CEP in the presence of photoionization during the pump pulse and of strong NA interactions. The dynamics is probed over time using a single XUV attosecond pulse, following both the evolution of the photoelectrons by velocity map imaging and by attosecond transient absorption spectra, providing information on the localization of the non-stationary electronic density and on the nuclear motion.
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